This invention relates to an apparatus and method for forming an optical element made of an ultraviolet hardening resin.
Optical elements, such as lenses used in optical devices including cameras and the like, are commonly made of glass or plastic. The optical elements made of plastic are light in weight, and are excellent in impact resistance and manufacturing cost as compared with those made of glass. Hence, the optical elements made of plastic are widely applied to numerous kinds of optical devices.
The optical elements made of plastic are known to be formed by using a thermoplastic resin, a thermosetting resin, or the ultraviolet hardening resin.
The optical elements made of the thermoplastic resin are formed by injection molding from the thermoplastic resin such as polymethyl methacrylate (PMMA) and polycarbonate (PC). In this method, there are drawbacks in internal homogeneity and in ability of transcribing the lens surface while mass production can be allowed for a short period of time.
The optical elements made of the thermosetting resin are formed by heat-polymerizing the thermosetting resin such as diethylene glycol bisaryl carbonate (CR-39) in a casting. This method is excellent in internal homogeneity and in ability of transcribing the lens surface; however, the method has a drawback of being poor in ability of mass production since it takes several hours and by extension several tens of hours for polymerization. In order to overcome the drawback encountered in the heat-polymerization in the liquid injection molding, a method for mass-producing the optical elements such as lens for a short period of time has been variously proposed, in which ultraviolet light is applied to the ultraviolet hardening resin from a light source such as a high-pressure mercury-vapor lamp and a metal halide lamp so as to induce polymerization to harden the ultraviolet hardening resin.
In the above-mentioned method for forming the optical elements in the use of the ultraviolet hardening resin, as a matter of course it is necessary to employ a forming mold through which ultraviolet light can be transmitted, such as glass. This is disclosed in Japanese Patent Provisional Publications Nos. 55-132221, 07-100835 and 08-1807, for example.